This invention concerns a fungicidal formulation and mildew-resistant paper; and more particularly a method for forming a mildew-resistant paper suitable for subsequent uses involving heat and moisture, and without involving quantities of hazardous solvents.
There are numerous problems presented in prior attempts to provide a satisfactory fungicidal cellulosic fiber mat, such as paper or multi-ply board for uses wherein the mat will be subjected to subsequent heat and humidity, for example when using the paper for the cover sheet of gypsum wallboard or in the formation of wallpaper and the like. In the formation and curing of gypsum wallboard, a slurry of gypsum and other materials is formed and, while wet prior to setting, is covered with paper facing sheets. Then when the gypsum is set, the combination is dried by heat and in the presence of considerable moisture. The cover sheets must be able to withstand the subsequent heat and moisture treatment without allowing the fungicide to become fugitive, that is vaporized or sublimated into the atmosphere. In addition, the paper sheets for such usage must be fungicidal without in any way interfering with the sizing activity.
There have been two basic prior approaches to incorporating a fungicide, in insoluble powdered or particulate form, into paper for such usage as in wallboard cover sheets; namely an interior or integral treatment method to the pump slurry during formation of the paper sheets, and a surface treatment method to the already formed paper. In the former method, which is currently the most commercially used method, the fungicide toxicant is added directly to the pulp slurry and, as a consequence, excessive amounts of fungicide are required to compensate for toxicant loss by fugitivity or sublimation on the paper machines and the board machines, plus water pollution is unavoidable due to fungicide wasted and lost in the waste water effluent system. In the latter application, if the fungicide is applied as an aqueous dispersion to normally sized paper, the fungicide generally adversely affects the paper sizing and almost doubles the normal quantity of sizing required. Further, there is a high degree of fungicide material loss due to "dusting" or fall-out at the paper mill rewinder, during shipping and handling, and once the paper has been formed in a final product mounted on walls or ceilings.
In addition most water base powder, paste or dispersion applications produce a vry uneven surface treatment. A very important criterion for surface treatment of the paper is that the fungicide deposited must uniformly and completely cover the paper surface. If there is any "spottiness" or non-uniform application of the fungicide material to the paper, a potential site for fungus growth is created. The treatment of paper which allows any such potential sites for fungus growth is really worse than no treatment of the pape at all, since additional time, chemicals, money, and processing have been put into the paper without achieving the desired result.
Many fungicides are available in soluble forms in solvent solutions or solvent emulsions; but these are unsuitable since evaporation of solvent creates both a fire and health hazard and any solvent remaining at the time the paper is applied to its intended usage, such as in gypsum paper and wallboard formation, adds health and fire hazards at that time.
A family of generally highly effective fungicides are the water-insoluble metal quinolinolate salts. The metal reactant to form the salt may be an alkaline earth metal, a heavy metal salt, or aluminum, tin or beryllium. Examples of suitable of such salts are the calcium, barium, magnesium, beryllium, lead, mercury, manganese, copper, nickel, iron, cadmium, silver, thallium, tin, zinc and aluminum salts of 2-hydroxyquinoline, 4-methyl-2-hydroxyquinoline, 4-hydroxyquinoline, 2-methyl-4-hydroxyquinoline; 5-hydroxyquinoline; 6-hydroxyquinoline; 7-hydroxyquinoline and 8-hydroxyquinoline. The preferred compounds for use in the present invention are the salts of 8-hydroxyquinoline; and particularly the copper-8-quinolinolate compound because it is commercially available and provides superior fungicidial and/or fungistatic properties. Copper-8-quinolinolate is a chelated copper organic salt having the following molecular structure: ##STR1## It is an odorless, amorphous fluffy green non-ionizable powder having a high degree of chemical stability and generally characterized by its low water and common organic solvent insolubility. Copper-8-quinolinolate has been solubilized with various organic materials such as set forth in U.S. Pat. Nos. 3,561,380; 2,608,556; 2,769,006; and 2,561,379. Copper-8-quinolinolate solubilized by these processes has compounded a material suitable for dilution with aromatic or aliphatic solvents for solvent applications to materials.
A paste emulsion concentrate of copper-8-quinolinolate has been propounded which may be thinned to use dilutions with water; however, the insoluble copper quickly settles out of the water dilutions. This paste emulsion suffers the detriments attributed to the un-solubilized copper-8-quinolinolate with regard to coating papers such as wallboard cover sheets. Hence, water dilutions of the paste emulsion concentrate, when applied to wallboard paper cover sheets by surface application result in uneven coverage and a speckled appearance due to spaces remaining between the particles of copper-8-quinolinolate, which spaces are susceptible to fungus attack; and only the surface immediately in contact with the copper-8-quinolinolate particles is protected. Further the copper-8-quinolinolate particles tend to "dust" out of the paper.